Is that noise inherent to film? Do webcams have the same noise?
The green channel has the least noise for Bayer-sensor digital cameras (which is almost all of them).
50% of the sensor sites are green (25% each for red and blue), so there is more signal given the same amount of noise.
Why do they make them like that? Why not make the sensors 33/33/33?
From Wikipedia on the Bayer Filter:
"Bryce Bayer's patent (U.S. Patent No. 3,971,065) in 1976 called the green photosensors luminance-sensitive elements and the red and blue ones chrominance-sensitive elements. He used twice as many green elements as red or blue to mimic the physiology of the human eye. The luminance perception of the human retina uses M and L cone cells combined, during daylight vision, which are most sensitive to green light."
The Foveon sensor does sample RGB at every pixel by using 3 layers, but it is only used in a few cameras.
I'm not sure either, but I can tell you that if you examine digitized (RGB) 35mm film -- across all 35mm film stocks -- the blue channel is the most noisy.
So my guess is: He might have chosen green over blue due to the blue channel being noisier.